EP0172731B1

EP0172731B1 - Classifier and controller for vertical mill

Info

Publication number: EP0172731B1
Application number: EP85305816A
Authority: EP
Inventors: Isao Hashimoto; Tosuke Kinoshita; Masahiro Uchida; Susumu Uchiyama
Original assignee: Kawasaki Jukogyo KK
Current assignee: Kawasaki Motors Ltd
Priority date: 1984-08-18
Filing date: 1985-08-15
Publication date: 1990-10-17
Anticipated expiration: 2005-08-15
Also published as: DK370385D0; EP0172731A3; US4684069A; DK370385A; JPS6150678A; JPH0464756B2; EP0172731A2; DE3580139D1

Description

The present invention relates to a classifier and its controller, the classifier being operable in a vertical mill, for example, to guide a powdery material by means of a gas flow, and to selectively draw off a portion of the powdery material according to the particle size of the powdery material.
Fig. 26 is a simplified sectional view showing a prior art static type of vertical mill 1. With reference to Fig. 26, in the case 1 a of the vertical mill 1 is mounted a table 2 having a vertical rotating axis, and the table 2 is rotated by a drive 3. This table 2 includes a table liner 2a for crushing powdery materials. Above the table liner 2a, a plurality of angularly spaced crushing rollers 4 are arranged around the circumference of the table. Each crushing roller 4 is rotatably connected to an arm 5 which swings on a pivotal axis 6 so that the angle between the table 2 and the arm 5 can be varied. An upper end of the arm is connected to a pressurizing device 7 which extends out of the casing 1a. This pressurizing means 7 presses on the arm 5 in an elastic manner thereby pressing the crushing roller 4 against the table liner 2a.
Above the table 2 is installed a feed tube 8 which feeds a raw material, such as a granular material, into the casing and onto the table. Further, above the table 2 is installed a classifier 9 which consts of a generally funnel-like cone 10 and classifying blades 11. In the top plate 12 of the casing 1a of the vertical mill 1, an outlet port 13 is provided for drawing the powdery material out of the casing 1a. In the casing 1a and beneath the table 2 are provided blast or intake ports 14 for supplying a gas flow around the table to raise the powdery material upwardly through the casing 1a, as will be explained later.
In a vertical mill 1 of the above-mentioned configuration, a powdery material fed through the feed tube 8 drops on the table 2. As the table 2 is rotated by the driving means 3, the powdery material is moved by the centrifugal action into a gap between the table liner 2a and the crushing rollers 4. The powdery material thus crushed between the table 2a and the crushing rollers 4 is caused to rise in the casing 1a by the gas being fed through the blast ports 14. The powdery material moves up around the outside of the cone 10 and enters, through a guide passage 15 between the cone 10 and the top plate 12, into the classifier through the blades 11. Upon entering, a portion of the powdery material, wherein the particle size is equal to or greater than a predetermined value, is driven downwardly by the classifying blades through the interior of the cone 10,. and is guided by the cone 10 and drops again on the table 2a. The portion of the powdery material of which the particle size is smaller than the predetermined value is lifted out of the casing 1a through the outlet port 13 by the gas flow from the blast port 14. The powdery material which drops through the cone 10 down to the table 2 is mixed with the powdery material being fed by the feed tube 8 and it is again crushed between the table liner 2a and the crushing rollers 4.
The vertical mill 1 which crushes material in the aforementioned manner is simple in construction, but it is not capable of producing, at the outlet port 13, a powdery material with an easily or freely-selected particle size distribution. In other words, the powdery material obtainable at the outlet port 13 can be adjusted in fineness (cm/g) so that it is not larger than a predetermined value by adjusting the angle of the classifying blades 11, but it is not possible to discharge a powdery material having a freely-selected particle size distribution.
Fig. 27 shows a simplified sectional view of another prior art rotary blade type of vertical mill 20, and Fig. 28 is a graph for explaining the classifying function of the vertical mill 20. This prior art mill is generally similar to the prior art mill shown in Fig. 26, and the corresponding parts are indicated by the same reference numbers. The present prior art mill is characterized in that a plurality of circumferentially spaced rotary blades 21 are provided in the upper portion of the casing 1a, in place of the cone 10 and the classifying blades 11 which constitute the classifier 9 of the prior art mill shown in Fig. 26.
The rotary blades 21 are secured, at their lower ends as shown in Fig. 27, to a support member 22, and the support member 22, in turn, is fixed to a rotary shaft 24 which is rotatably driven by a drive 23.
In the vertical mill 20 of the above-mentioned configuration, a powdery material fed into the mill by the feed tube 8 rises, after passing through the processes similar to those described in connection with Fig. 26, in the casing 1 a. In rising, the powdery material moves in such a manner as to pass, together with the gas from the blast port 14, through the spaces between the plurality of rotating blades 21. Since the blades 21 are being driven to rotate as explained above, a portion of the powdery material, the particle size of which is greater than a certain predetermined value, is given a large centrifugal force and forced to drop downwardly in the casing 1a. On the other hand, the portion of the powdery material the particle size of which is equal to or smaller than the predetermined value, passes through the spaces between the rotary blades 21 and moves out of the casing 1a through the outlet port 13. The portion of the powdery material having the excessive particle size, which drops downwardly in the casing 1a, is crushed again on the table 2.
The vertical mill 20 of the above-mentioned configuration is capable of adjusting the particle size of the powdery material leaving the outlet port 13 by altering the rotational speed of the rotary blades 21. With reference to Fig. 27, when the rotary blades 21 are rotating at a constant speed, the cumulative value of particle size distribution plotted against particle diameter, according ot Rosin-Rammler, is indicated by the line 100 of Fig. 28 for the powdery material obtained at the outlet port 13.
When the rotational speed of the rotary blades 21 is reduced, the Rosin-Rammler plot of cumulative particle size distribution of the powdery material leaving the outlet port 13 will be as shown by the line 101 of Fig. 28. If the angle between the line 100 and the axis of the abscissa, and the angle between the line 101 and the axis of the abscissa are denoted by 61 and 82 respectively, the tangential values N obtained from 01 and 82 are expressed by the following equations:
As shown in Fig. 28, the values N representing the distribution of particle diameters of the powdery material satisfy the following relation:
Although a predetermined fineness (cm²/g) can be freely selected by changing the rotational speed of the rotary blades 21, it is not possible to obtain a freely selected distribution of particle sizes of the powdery material. In Fig. 28, the fineness of the powdery material of the line 100 is higher than that of the line 101 since the overall particle sizes of the line 100 are smaller than those of the line 101. However, it is not possible to adjust N, and N₂ of these lines. In the case of Fig. 26, the angular adjustment of the classifying blades 11 corresponds in results obtained to the rotational speed adjustment of the rotary blades 21 shown in Fig. 27.
In the vertical mill 20 shown in Fig. 27, when cement clinker for example, is to be crushed, it is desirable, in view of the strength achieved when water is added to the cement, and the attendant cost, to set the value of N, and accordingly the distribution of the particle sizes of the powdery . material as shown in Fig. 28, so that the powdery material has a considerable range of particle sizes. In the vertical mill 20, however, since the crushing time of the powdery material is short, there is a problem in that the portion of the powdery material which circulates in the casing 1a becomes larger, and in turn the value N gets larger, or the distribution of the particle sizes of the powdery material obtainable at the outlet port 13 is extremely narrow.
Fig. 29 is a simplified sectional view of a prior art static-rotary blade type vertical mill 30. Corresponding parts of the vertical mill 30, which are similar to the above-mentioned prior art mills, are denoted by the same reference numbers. In this prior art vertical mill 30, a classifier 9 consisting of a cone 10 and classifying blades 11 such as those shown in Fig. 26, and the rotary blades 21 such as those shown in Fig. 27, are installed in combination. The raw material, fed through the feed port 8, rises as powdery material in the casing 1 a, through the processes explained in connection with the above-mentioned prior art mills. The powdery material thus raised is guided into the cone 10 through a guide passage 15 and between the classifying blades 11. Upon entry, a portion of the powdery material of which the particle sizes are equal to or greater than a predetermined particle size, is dropped by the classifying blades 11 along the inner wall of the cone 10 to be collected on the table 2. The portion of the powdery material which has not been so collected is classified, as explained above, by the rotary blades 21 which are driven by the drive 23, and the powdery material thus classified is taken out of the casing 1a through the outlet port 13. The remaining portion of the powdery material drops through the cone 10 onto the table 2 and is again crushed.
The vertical mill 30 of such a configuration also has a problem similar to that pointed out for the vertical mill 20 of Fig. 27. Namely, the distribution of the particle sizes of the powdery material obtainable at the outlet port 13 is narrow, and changing the speed of rotation of the rotary blades 21 changes the central or average value of the particle size distribution of the powdery material, but not the range of particle size distribution of the powdery material; a freely selected range of distribution cannot be obtained.
Thus the problem common to the prior art mills is that it is difficult to adjust the range of distribution of the particle sizes of the powdery material obtainable from the outlet port 13 at any desired level to suit the intended use of the powdery material.
Therefore it is a primary objective of the present invention to provide a classifier and a controller therefor, the classifier being capable of solving the above-mentioned problem and of freely setting the range of the particle size distribution of the powdery material from the classifier at a predetermined desired value.
According to the preamble of claim 1 and as disclosed in JP-A-59-120256, there is provided a classifier for a vertical mill, the mill including an outer casing having a top plate and an associated exit for powdery material, means in the lower portion of the casing for pulverising material, and means producing an upward flow of gas for carrying powdery material upwardly toward the top plate, said classifier comprising a rotary impeller, especially a set of impeller blades, in said casing adjacent said top plate and having a generally vertical axis of rotation; according to the invention said rotary impeller is spaced below said top plate to provide a gap between said rotary impeller and the top plate, and an annular impingement member is mounted under the top plate and outwardly surrounding the upper portion of said rotary impeller so as to shield said gap, said annular impingement member having an opening or openings associated therewith through which gas and powdery material can pass radially inwardly en route to said exit without passing through said impeller.
In a preferred embodiment, a roller mill and a classifier therefor in accordance with this invention includes a casing having a top plate, the classifier being adjacent the top plate. Beneath the top plate, upon which impinges the gas and the powdery material being supplied from the lower portion of the casing, is provided a rotary impeller comprising a plurality of rotary blades or rods which have a vertical axis of rotation. A gap is provided between the rotary blades and the top plate, and the annular impingement member is suspended from the top of the casing to outwardly surround the upper portion of the plurality of rotary blades in such a way as to shield the gap. Further, an opening is provided in the impingement member through which a portion of the gas and powdery material passes.
Further, the present invention may include a controllerfortheclassifier,the controller including means for adjusting the opening through which the powdery material passes. A collecting means is provided for collecting powdery material from the classifier, including a detecting means for detecting the distribution of the particle sizes of the powdery material received by the collecting means and giving an output signal related to the distribution, and means for changing said output signal in the direction toward a predetermined value are activated by the output signal, the size of the opening being varied by said means for adjusting the opening.
During the operation of the apparatus, the gas and the powdery material supplied from the lower portion of the casing rise through the casing, and a portion of the powdery material is classified by the rotating blades. In other words, a portion of powdery material having larger particle sizes is given a larger centrifugal force due to impingement on the rotary blades, etc., and these particles descend in the casing. Another portion of powdery material of smaller particle sizes passes through the gaps of the rotary blades and enters an interior space defined by the plurality of rotary blades.
A portion of powdery material not moving towards the rotary blades impinges on the annular .impingement member hanging from the top plate and outwardly surrounding the rotary blades, and a part of this remaining portion drops in the casing and becomes classified by said rotary blades.
A portion of the powdery material impinging on the impingement member passes through the opening to the outlet port without being classified by the rotary blades.
Accordingly, the powdery material passing through the opening contains some powdery material of larger particle sizes which has not been classified by the plurality of rotary blades. Thus, the powdery material having passed through the classifier and some having passed through said opening are mixed together and exit from the casing. The powdery material thus leaving the casing is collected by a collecting means. A value corresponding to the particle size distribution of the collected powdery material is then sensed by a detecting means, and means as aforesaid is activated for adjusting the particle size distribution of the powdery material so that the detected value matches a predetermined value. The adjusting means can adjust the size of the flow passage through the impingement member and/or the rotary blade speed, to achieve this particle size distribution adjustment.
The invention will be better understood from the following description taken in conjunction with the accompanying drawings wherein:

Fig. 1 is a sectional view of a vertical mill according to a first embodiment of the present invention;
Fig. 2 is a simplified perspective view of the upper portion of the vertical mill;
Fig. 3 is a simplified plan view of the upper portion of the vertical mill;
Fig. 4 is a perspective view of an impingement member;
Fig. 5 is a set of graphs for explaining the operating conditions of the vertical mill;
Fig. 6 is a set of graphs for explaining the functioning of a classifier;
Fig. 7 is a sectional view of a vertical mill according to a second embodiment of the present invention;
Fig. 8 is an exploded perspective view of a part of an impingement member of a third embodiment of the present invention;
Fig. 8A is a sectional view taken along the section line 8A-8A of Fig. 8;
Fig. 9 is a plan view of the impingement member of Fig. 8;
Fig. 10 is a front view of a part of the impingement member of Fig. 9;
Fig. 11 is a sectional viewtaken along the section line 11-11 of Fig. 9;
Fig. 12 is a simplified perspective view of a vertical mill according to a fourth embodiment of the present invention;
Fig. 13 is a sectional viewtaken along the section line 13-13 of Fig. 12;
Fig. 14 is a simplified perspective view of a vertical mill according to a fifth embodiment of the present invention;
Fig. 15 is a sectional view along the section line 15-15 of Fig. 14;
Fig. 16 is a simplified sectional view of a portion of a classifier for a vertical mill according to a sixth embodiment of the present invention;
Fig. 17 is a simplified perspective view of a portion of a classifier for a vertical mill according to a seventh embodiment of the present invention;
Fig. 18 is a perspective view of a portion of the vertical mill of Fig. 17, taken near a top plate of the mill;
Fig. 19 is a sectional view of a portion of a classifier for a vertical mill according to an eighth embodiment of the present invention;
Fig. 20 is a plan view of a part of the classifier of Fig. 19;
Fig. 21 is a sectional view of a vertical mill according to a ninth embodiment of the present invention;
Fig. 22 is a simplified plan view illustrating the configuration of an impingement member of a vertical mill;
Fig. 23 is a simplified plan view of the vertical mill;
Figs. 24 and 24A are sectional views illustrating the configuration of the impingement member;
Fig. 25 is a system diagram of a controller of a classifier according to another embodiment of the present invention;
Fig. 26 is a simplified sectional view of a prior art static type vertical mill;
Fig. 27 is a simplified sectional view of another prior art rotary blade type vertical mill;
Fig. 28 is a graph illustrating the classifying function of the vertical mill of Fig. 27; and
Fig. 29 is a simplified sectional view of another prior art static-rotary blade type vertical mill.

With reference to Figs. 1 through 4, the vertical mill 40 includes a casing 41, a rotary table 42 having a central vertical axis of rotation being located within the casing, and the table is arranged to be rotatively driven by a drive 43 having a power shaft 43a.
The table 42 consists of a table body 42a and an annular table liner 42b fixed to the outer periphery of the table body 42a, the liner having an annular groove. Above the table liner 42b, a plurality of angularly spaced freely rotatable rollers 44 are located.
A support shaft 45 of each crushing roller 44 is connected to an arm 46 which is movable on a pivot pin 47 so that the angle between the support shaft 45 and the table can be varied. The end of the arm 46, opposite to the pivot pin 47, is connected to a pressurizing means 48 which extends outward from a hole in the casing 41. This pressurizing means 48 elastically presses against the arm 46, and consequently the crushing roller 44 is pressed toward the table liner 42b.
Beneath the table 42 and within the casing 41, a gas intake or blast port 49 is provided to feed a gas for blowing upwardly in the casing and carrying a powdery material as will be explained later. The gas fed from the blast port 49 passes through an annular gas conducting passage 50, . such as a duct installed beneath the table 42 and surrounding the table 42, and the gas blows up from below the table 42 and all around the circumference of the table. In the casing 41 and above the table 42, a material feed tube 51 which feeds the raw material onto the table 42 extends outward through a hole in the casing 41.
Further, above the table 42 and adjacent a top plate 57 of the casing, a plurality of angularly spaced rotary blades 52 having a vertical axis of rotation are provided. The lower ends of the rotary blades 52 are fixed to a disc 53 around the disc circumference. The rotary blades 52 are flat (see Fig. 2) and extend radially outward and upwardly towards the top plate 57 of the casing 41, and their upper ends are fixed to an annular ring member 54. Attached to the center of the disc 53 is a drive shaft 56 which is rotatively driven by a driving means 55 (Fig. 1). A gap 57a of a predetermined size is intentionally provided between the ring member 54 and the top plate 57.
An annular impingement member 58 is provided, hanging from the top plate 57 of the casing 41, and outwardly surrounding the upper portion of the rotary blades 52 and the member 54, thereby shielding the above-mentioned gap 57a. With reference to Fig. 5, the function of the impingement member 58 will now be explained. The impingement member 58 has an approximately cylindrical part 59 which externally surrounds the rotary blades 52, and the cylinder part 59 is a little longer than the above-mentioned gap 57a; a flange 60 of the member 58 is fixed to the top plate 57. In the flange 60, a plurality of through holes 61 are formed, and by means of these through holes the impingement member 58 is secured to the top plate 57 by means of bolts (not illustrated). Further, in the cylinder 59, an opening 62 is formed to provide a gap or opening through which powdery material of relatively large particle sizes is removed, as will be explained later.
This impingement member 58 and the above-mentioned rotary blades 52 essentially constitute a classifier 63, and the powdery material having passed through the classifier 63 is discharged from an outlet port 64 in the top plate 57.
The operation of the vertical mill 40 having the above-mentioned configuration will now be explained. With reference to Fig. 1, the raw material to be pulverised is fed by the feed tube 51 and drops on to the rotating table 42. As the table 42 is rotated by the driving means 43, the material on the table 42, under the influence of the centrifugal force, moves into the groove and towards the space between the table liner 42b and the crushing rollers 44 where the material is crushed. The crushed powdery material rises in the casing 41 due to the gas flow through the passage 50 and the blast port 49. For the powdery material immediately after crushing, the percent weight of powdery material plotted against particle diameter is shown by the curve 202 of Fig. 5A. The point P1 on the abscissa of Fig. 5A shows the central or average value of the particle size of the powdery material after crushing.
A portion of the powdery material rising in the casing 41 moves, following the stream of the gas, through the gaps in between the rotary blades 52, and in the process, a part of the powdery material is given a radially outward momentum. Of this part of the powdery material, a portion of the powdery material having particle sizes greater than a certain particle size, which is predetermined by the velocity of the gas flow, the rate of rotation of the rotary blades, etc. escapes from the gas stream and drops in the casing 41. This dropped powdery material falls on to the table 42 and is crushed once again together with new material added by the tube 51.
For the powdery material that has passed through the above-mentioned rotary blades 52, the percent weight of powdery material plotted against particle diameter is indicated by the line 203 of Fig. 5B. The line 203a shows a similar distribution in which the rate of rotation of the rotary blades 52 is greater than that represented by the case of the line 203. The points P2 and P2a on the abscissa are the respective central or average values of the particle size in each case. When the line 203 of Fig. 58 is compared with the line 202 of Fig. 5A, it is seen that the powdery material that has passed through the rotary blades 52 consists of a portion of relatively smaller particle sizes extracted from the total of the powdery material crushed by the crushing rollers 44.
A part of the powdery material rising in the casing 41. impinges on the impingement member 58. Of this portion of the powdery material, a portion of the powdery material which passes through the opening 62 formed in the impingement member 58 is not classified by the rotary blades 52, and it moves through the gap 57a between the member 54 and the top plate 57, and it moves into a central space 65 defined by the rotary blades 52, the disc 53 and the ring member 54, or towards the outlet port 64. For the powdery material that has passed through the opening 62, the percent weight of the material plotted against particle diameter is shown by the line 204 of Fig. 5C. It is seen that this portion of the powdery material contains particles of which the particle sizes are greater than those of the powdery material which has passed through the gaps in between the rotary blades 52 as shown by Fig. 5B.
As discussed above, powdery material which has passed through the opening 62 mixes with the powdery material which has been classified by and passed through the rotary blades 52 and has entered into the space 65, and the mixture exits from the casing 41 through the outlet port 64. For this exiting mixture, the percent weight of powdery material plotted against particle diameter is shown by the curve 205 of Fig. 5D. The point P4 on the abscissa is the average or central value of the particle size for the curve 205. The curve 206 shows the particle size distribution when the effect of the opening 62 is not present, the classification is effected by the rotary blades 52 alone, and the rate of rotation of the rotary blades 52 is adjusted so that the average or central value of the particle size of the powdery material becomes P4.
The curves of Fig. 5D show that the size distribution of the powdery material obtainable at the outlet port 64 contains, as explained above, a wide range of particle sizes.
The curve 207 of Fig. 5E shows the size distribution of the powdery material which is classified by the rotary blades 52 and drops in the casing 41 without moving into the space 65. Such powder material contains relatively larger particle sizes of the powdery material.
Fig. 6A is a Rosin-Rammler plot of the curves 203 and 204 of Figs. 5B and 5C, and Fig. 6B is a similar plot of the curve 205 of Fig. 5D. The line 208 and the line 209 of Fig. 6A correspond to the curve 203 of Fig. 5B and the curve 204 of Fig. 5C, respectively. The angles made by the lines 209 and 208 with the abscissa are 83 and θ4, respec- tiνely,and their tangential values are N3 and N4. Similar for the angle 05 of line 210 of Fig. 6B.
The following relations are established between the tangential value N5 of the angle 65 which is made by the line 210 of Fig. 6B with the abscissa and the tangential values N3 and N4 of the above-mentioned angles 63 and 94;

In other words, in the present embodiment of the invention, it is possible to obtain a powdery material having a wide range of particle size distribution with a selected central value of particle size by selecting the central particle diameters P2 and P3.
Fig. 7 is a sectional view of a vertical mill 70 according to the second embodiment of the present invention, which is generally similar to the preceding embodiment. The corresponding parts are given the same reference numbers. It should be noted that, in the present embodiment, within the casing 41 are provided an approximately funnel-shaped cone 71 and classifying blades 72, and the cone 71, the classifying blades 72, rotary blades 52 and an impingement member 58 essentially constitute a classifier 73.
The cone 71 is an inverted cone in shape, and is provided coaxially above the table 42. At the apex of the cone, which is the closest part to the table 42, a drop port 74 is formed for dropping powdery material as will be explained later. In the upper interior of the cone 7 of Fig. 7, a plurality of classifying blades 72 which are circumferentially arranged on a vertical axis are provided. Inside the cone 71 and the classifying blades 72 are also provided rotary blades 52 and an impingement member 58 having a configuration similar to that of the first embodiment.
The operation of the vertical mill of Fig. 7 is generally similar to that of Fig. 1 and is as follows: Raw material is fed by a feed tube 51 onto the table and crushed between a table liner 42b and crushing rollers 44. The distribution by weight of the powdery material, which has been crushed but not classified as yet, according to the particle size is as shown by the curve 202 of Fig. 5A. The crushed powdery material, rising with the gas flow from the blast port 49, rises in the casing and is guided to the classifying blades 72 near the top of the cone 71.
The classifying blades 72 are angled to impart a swirl to the gas being guided into the cone 71. As a swirling flow is generated and directed towards the center of the cone by the classifying blades 72, the powdery material being carried by the gas is given a centrifugal force. Accordingly, particles of larger diameters reach the wall of the cone 71 and collect towards the drop port 74. The particles drop through the drop port 74 and onto the table 42. On the table 42, the powdery material is mixed with raw material from the feed tube 51 and is crushed again. The classifying blades 72 thus make the first classification and remove the coarse particles having very large diameters. The strength of the gas swirl is adjustable by turning the support rods 72a which fasten the blades 72 to the top plate 57 and thereby adjusting the mounting angle of the classifying blades 72. The greater the angle and the swirling force, the finer will be the classified powdery material.
In the cone 71, the powdery material moving to the rotary blades 52 is again classified as described in connection with the first embodiment, and a portion of the material descends in the cone 71 and drops upon the table 42, and the remaining portion enters the space 65. The distribution by weight of the powdery material inside the space 65 according to the particle diameter is as indicated by the lines 203 and 203a of Fig. 5B.
Now, in the cone 71, a portion of the powdery material enters the space 65 through the opening 62 formed in the impingement member 58. Since this portion of the powdery material having entered the space 65 has not been classified by the rotary blades 52, it contains many particles of larger diameters. The weight distribution according to the particle size is indicated by the curve 204 of Fig. 5C.
In the outlet port 64, the powdery material having passed through the rotary blades 52 and the powdery material having passed through the opening 62 are mixed together, and the mixture has a weight distribution which is indicated by the curve 205 of Fig. 5D. The rotary blades 52 and the impingement member 58 thus execute a secondary classification. As a result of these classifications, the weight distribution of the powdery material dropping in the cone 71 is as shown by the curve 207 of Fig. 5E. Further, when the rate of rotation of the rotary blades 52 is altered, effects similar to those described in connection with the first embodiment, with specific reference to Fig. 6, are observed.
The powdery material in the space 65 after the above-mentioned classifications is removed from the casing 41 through the outlet port 64.
In the present embodiment of Fig. 7, classification with a central or average value of selected particle size and a wide range of particle size distribution is achieved, since the classifier 73 is essentially constituted by the cone 71, the classifying blades 72, the rotary blades 52 and the impingement member 58.
Figs. 8 to 11 show an impingement member 58 of the third embodiment of the present invention. The present embodiment is generally similar to the above-mentioned embodiments and the corresponding parts are given the same reference numbers. The overall configuration of the impingement member 58 is similar to that of an inverted hat without a bottom (see Fig. 4). The impingement member 58 consists, for example, of three arcuate sections 58a, 58b and 58c of the same shape (see Fig. 9), and the three sections are fixed to the top plate through a plurality of through holes 61 with bolts (not illustrated).
The member section 58b, for example, has an opening 62. Further, the member section 58b, for example, is provided with a plurality of through holes 76 (Fig. 8). A cover 77 is provided to partially cover the opening 62, and the cover 77 is provided with through holes 78. By meamy of the through holes 78 and 76, the cover 77 can be fixed to the impingement member 58b with, for example, screws 79. The bottom of the cover 77 is arranged to ride on the top of a guide plate 75, and the cover can slide over the top. The cover 77 and the impingement member 58 are arranged so that a portion of the opening 62 through which the powdery material, etc. passes, or the area of the opening 62, can be varied by shifting the position of the cover 77 over the opening 62 and matching the through holes 78 to any desired through holes 76 and fixing them together with the screws 79.
It, therefore, is possible to alter the quantity of the powdery material which enters the impingement member 58 by altering the area of the passage 80 (Fig. 10) which is the uncovered part of the opening 62. The product A collected at the outlet port 64 (having the particle diameter distribution of the curve 205 of Fig. 5D) is a mixture of the product B which passes through the rotary blades 52 and contains much fine powder (having the particle diameter distribution of the curve 203 of Fig. 5B), and the product C, which contains coarse powder from the opening 62 (having the distribution of the curve 204 of Fig. 5C); and the proportion of the product C in the product A is altered by adjusting the area of the opening 62. Thus, it is possible to adjust the quantity of coarse powder of the curve 205 of Fig. 5D. As it is also possible to adjust the width of the particle size distribution of the line 205 by adjusting the speed of the rotary blades 52, the size of the average diameter value P5 of the product A (having the particle diameter distribution of the curve 207 of Fig. 5E) can be selected.
Fig. 12 is a simplified perspective view of the vertical mill 81 of the fourth embodiment of the present invention, and Fig. 13 is a sectional view along the line 13-13 of Fig. 12. This present embodiment is similar to, for example, the above-mentioned first embodiment, and the corresponding parts are given the same reference numbers. Since the basic configuration of the vertical mill 81 of the present embodiment is similar to that of the vertical mill 40 illustrated in Fig. 1, only special points of difference are described.
One point to note with respect to the present embodiment is that a cylindrical plate, instead of the impingement member 58 fixed to the top plate 57 as shown in Fig. 1, is used as the impingement member 58, and it is fixed to a plurality of rods 83 which are driven individually by a plurality of hydraulic cylinders 82 to extend or retract. The impingement member 58 thus is arranged to be shifted parallel to its axis, or toward and away from the top plate, by the hydraulic cylinders 82. In this arrangement, each rotary blade 52 is arranged to have a clearance 57a of L1 in height between the upper end of the blade 52 and the top plate 57. The height L1 of the clearance 57a is at least sufficient to allow coarse particles, which are indicated by the curve 204 of Fig. 5C of the first embodiment, to flow without clogging.
The edge of the impingement member 58 which is on the side adjacent the rods 83 has a clearance 85 (Fig. 13) of L2 in height from the top plate 57 all around the circumference, and this height L2 can be altered by means of the hydraulic cylinders 82. Accordingly, the quantity of the powdery material which flows into the space 65 through the clearances 85 and 57a can be adjusted by adjusting the height L2 of the clearance 85. In other words, of the powdery material having the distribution of Fig. 5A of the first embodiment, the portion having passed through the rotary blades 52 has a distribution indicated by the curve 203 of Fig. 5B, and the portion having passed through the clearances 85 and 57a is represented in Fig. 5C. These powdery materials with different average values of particle diameter are mixed together in the space 65 or at the outlet port 64 to obtain the distribution curve indicated by Fig. 5D.
Further, the present embodiment has a classifying capacity which allows selection of the distribution range of the particle diameter with an average value of particle diameter which is also selectable, by altering the height L2 of the clearance 85 and the rate of rotation of the rotary blades 52.
In the above-mentioned embodiment, the impingement member 58 is movable by hydraulic cylinders 82. It may instead be shifted by other means such as screws in place of the hydraulic cylinders 82.
Fig. 14 shows a simplified perspective view of a vertical mill including the fifth embodiment of the present invention, and Fig. 15 is a sectional view along the line 15-15 of Fig. 14. The present embodiment is similar, for example, to the above-mentioned fourth embodiment, and the corresponding parts are given the same numbers. Since the basic configuration of the vertical mill 86 of the present embodiment is similar to that of Fig. 12, only special points of interest are described.
One point to note in the present embodiment is that an annular shield member 87 is fixed at one edge to the top plate 57 and hangs from the top plate 57, in the space between the rotary blades 52 and the impingement member 58. The vertical height L3 of the shield member 87 is arranged to be shorter than the height L1 of the clearance between the rotary blades 52 and the top plate 57. The distance L2 between the impingement member 58 and the top plate 57 can be adjusted by, for instance, vertically displacing the impingement member 58 as shown in Fig. 15 by the extension or contraction of the rods 83 of the hydraulic cylinders 82.
With this arrangement, a portion of the powdery material near the top plate enters the central space 65 through the clearance 85 between the impingement member 58 and the top plate 57, and through the clearance 88 between the shield member 87 and the rotary blades 52. Thus, a powdery material having a broad range of distribution indicated by the curve 205 of Fig. 5D can be obtained. Further, the present embodiment has a classifying capacity which allows selection of the distribution range of the particle diameter, with an average value of particle diameter that is also selected, by altering the height L2 of the clearance 85.
Fig. 16 is a simplified perspective view of a vertical mill of the sixth embodiment of the present invention, showing the classifier 63. The present embodiment is similar for example, to the above-mentioned first embodiment, and the corresponding parts are given the same numbers. As the basic configuration of the vertical mill of the present embodiment is generally similar to that of Fig. 1, only special points of interest are described. One point to note in the present embodiment is that an annular movable shield ring 90 is provided, the movable shield ring 90 externally surrounding the impingement member 58 which in turn externally surrounds the rotary blades 52.
The movable shield member 90 is fixed, for example, to rods 83 which are driven by the hydraulic cylinders 82 to extend or contact. The movable shield member 90, therefore, can be moved parallel to its axis (the vertical direction in Fig. 16), and the height L4 of the clearance 91 with the top plate 57 can be selected.
The movable shield member 90 externally surrounds the impingement member 58 as explained above, and it is arranged to cover the opening 62 formed in the impingement member 58. Accordingly, the area of the opening 62 for the passage of the powdery material can be adjusted by adjusting the height L4 of the clearance 91. The powdery material having passed through the opening 62 for the passage of the powdery material has not been classified by the rotary blades 52, and has a size distribution as indicated by the curve 204 of Fig. 5C. The powdery material having entered the space 65 or reaching the outlet port 64 via the opening 62 is then mixed with the powdery material having been classified by the rotary blades 52 and having the size distribution shown by the line 203 of Fig. 5B to obtain the size distribution shown by the line 205 of Fig. 5D.
Further, since the height L4 of the clearance 91 is variable as explained above, the present embodiment has a classifying capability which allows selection of the width of the distribution curve of particle diameter with an average value of particle diameter also selected.
In the above-mentioned embodiment, the movable shield member 90 is moved by hydraulic cylinders 82, but it may instead be arranged to be moved by screws in place of the hydraulic cylinders 82.
Fig. 17 is a simplified perspective view of a portion of a classifier for a vertical mill of the seventh embodiment of the present invention. Fig. 18 is a perspective view of a portion of the vertical mill of Fig. 17, adjacentthetop plate of the mill. The present embodiment is similar, for example, to the above-mentioned first embodiment of the present invention, and the corresponding parts are given the same reference numbers. As the basic configuration of the vertical mill of the present embodiment is similar to that of Fig. 1, only points of several interest are described. One point to note in the present embodiment is that a movable cover 95 is provided, the movable cover being capable of at least partially covering the opening 62 in the impingement member 58 which externally surrounds the rotary blades 52.
With reference to Figs. 17 and 18, to the top end of the movable cover 95, which is capable of at least partially covering the opening 62 in the impingement member 58, are fixed the lower ends of connecting rods 96a and 96b. The other ends of the connecting rods 96a and 96b extend through arcuate slits 97a and 97b in thetop plate 57 and are fixed to a movable arcuate support member 98. The movable support member 98 is arranged to cover the slits 97a and 97b, and it is capable of preventing the powdery material being contained beneath the top piate 57 from leaking outofthetop plate. Further, the movable cover 95 can be shifted circumferentially relative to the opening 62 by shifting the movable support member 98 in the circumferential direction.
The area of the opening 62 for passage of the powdery material can be altered by shifting the movable cover 95 of the above-mentioned configuration circumferentially around the axis of the impingement member 58 using the support 98 and altering the degree of covering of the opening 62.
Further, as the powdery material having passed through the above-mentioned passage area of the opening 62 has not been classified by the rotary blades 52, the powdery material has a weight distribution having a relatively large quantity of coarse powder. The distribution is indicated by the curve 204 of Fig. 5C. The powdery material entering the space 65 after the classification by the rotary blades 52 has, as explained above, a weight distribution indicated by the line 203 of Fig. 5B, which contains much fine powder. In the space 65, these powdery materials are mixed together to produce a powdery material of which the weight distribution is as indicated by the line 205 of Fig. 5D.
Further, as the area of the flow passage of the opening 62 can be altered by means of the movable cover 95, together with the capability of adjusting the velocity of rotation of the rotary blades 52, the present embodiment has a classifying capability which allows selection of the width of the particle diameter distribution, with an average value of particle diameter also selected.
Fig. 19 is a sectional view of a portion of a classifier 63 for a vertical mill of the eighth embodiment of the present invention, and Fig. 20 is a plan view of a part of the classifier 63. The present embodiment is similar, for example, to the above-mentioned seventh embodiment of the present invention, and the corresponding parts are given the same reference numbers. As the basic configuration of the vertical mill of the present embodiment is similar to that of Fig. 17, only points of special interest are described. A point to note of the present embodiment is that an arcuate movable cover 95 is provided, this movable cover being capable of moving to at least partially cover the opening 62 in the impingement member 58 which externally surrounds the rotary blades 52. A rack 100 is provided on a part of the movable cover 95 so that the movable cover 95 can be freely displaced along the circumference of the impingement member 58 by a rotatable pinion 102 which is rotatively driven by a driving means 101.
To the lower part of the impingement member 58 of Fig. 19 is fixed a guide member 103 which extends along the circumference of the impingement member 58. Along the outer circumference of the impingement member 58, the movable cover 95 is provided so that the cover is guided by the guide member 103. In the outer circumference of the movable cover 95 is formed the rack 100. The pinion 102 engages the rack 100 and is fixed to a rotary shaft 104, and the shaft and the pinion are rotatively driven clockwise or counterclockwise by the driving means 101.
In a classifier 63 of such an arrangement, the movable cover 95 can be circumferentially displaced by rotatively driving the pinion 102 using the driving means 101. The area of the opening 62 which is open for passage of the powdery material thus can be altered by moving the cover 95.
The powdery material moving through the passage of the opening 62 of the classifier 63, having the above-mentioned functions, has a distribution indicated by the curve 204 of Fig. 5C because the powdery material has not been subjected to the classification by the rotary blades 52. The powdery material entering the space 65 after classification by the rotary blades 52 has a distribution indicated by the curve 203 of Fig. 5B as explained in connection with the preceding embodiment. These powdery materials are mixed together in the space 65 or at the outlet port 64 to produce a distribution indicated by the curve 205 of Fig. 5D.
Further, as the area of the passage of the opening 62 can be altered by shifting the position of the movable cover 95, the present embodiment has a classifying capability which allows selection of the range of the particle diameter distribution curve, with an average value of particle diameter being also selected.
Fig. 21 is a sectional view of a vertical mill 110 according to the ninth embodiment of the present invention; Fig. 22 is a simplified plan view for explaining the configuration of an impingement member 58 of the vertical mill 110; Fig. 23 is a simplified plan view of the vertical mill 110, and Fig. 24 is a sectional view for further explaining the configuration of the impingement member 58. The present embodiment is similar, for example, to the above-mentioned first embodiment of the present invention, and the corresponding parts are given the same reference numbers. As the basic configuration of the vertical mill 110 of the present embodiment is similar to that of Fig. 1, only points of special interest will be described.
A point to note of the present embodiment is that the impingement member 58 is provided in the form of a large number of impingement pieces, for example, rectangular plates 111a, 112b, nic,... (hereinafter generally referred to by the reference number 111). The impingement pieces are arranged circumferentially of the rotary blades 52 in sequence. As shown in Fig. 22, each impingement piece 111 has, on the outer end, a rotational shaft 112 having a vertical axis of rotation.
Referring to Figs. 23 and 24, the rotational shaft 112a, for example, is positioned through a through hole 113a in the top plate 57 and projects upwardly out of the top plate 57. The through hole 113a is provided with a bearing member 114a such as a ball bearing to assure smooth rotation of the rotational shaft 112a and to prevent leakage of the powdery material from the casing 41 (see Fig. 21). At the through hole 113a, an annular washer 115a, for example, is fastened to the top plate 57. The bearing member 114a, therefore, is fixed in the through hole 113a.
The rotational shaft 112a is fixed, near its upper end, to one end of the connecting member 116a. On the other end of the connecting member 116a, a pivotal shaft 117a is rotatively placed through the connecting member, in parallel with the axis of rotation of the rotational shaft 112a. This pivotal shaft 117 is rotatively placed through the connecting member 116a and an annular member 118, and is secured with, for example, a nut 119a . to prevent detachment.
The remaining impingement pieces 111b, 111c,... and the components related thereto have a configuration similar to the above- described configuration of the impingement piece 111a a (the generic reference numbers for the reference numbers 111ato 117a and 119a are 111 to 117 and 119, respectively). The annular ring 118 thus connects with all the pivotal shafts 117a, 117b,... An arm 120 is provided on the outer circumference of the annular ring 118, and a connecting piece 121, which is provided on the arm on the opposite end to the annular ring 118, is connected to a connecting link 122 by a pin in such a way that the angle between the projection and the connecting member 122 can be freely varied.
The end of the connecting member 122, which is opposite to the connecting piece 121, is connected to one end of a rod 124 by a pin, the rod being extended and contracted by a driving means 123 such as a hydraulic cylinder.
The operation of the vertical mill of the above-mentioned configuration is as follows. As explained in the first embodiment, a portion of the powdery material which has been crushed and rises in the casing 41 is classified by the rotary blades 52, and enters the space 65. Another portion enters, via the impingement member 58, the space 65 or the outlet port 64.
The impingement member 58 may, as shown in Fig. 22, have a gap 125a, 125b ... (the generic reference number is 125) between two adjacent impingement pieces 111. The displacement of the rod 124 and of the connecting piece 122 being reciprocatively driven in the direction of the arrow A of Fig. 23 by the driving means 123, is converted into a circumferential displacement of the annular ring 118 because the connecting member 122 is connected to the connecting piece 121 in such a way that the angle between them can be varied.
In Fig. 23, when the annular ring 118 is circumferentially displaced in the direction of the arrow B or the arrow C, the respective connecting members 116 and the respective rotational shafts 112 will be angularly displaced in the direction of the arrow D or the arrow E, respectively. With reference to Fig. 22, when the respective rotational shafts 112 are angularly displaced in the direction of the arrow D, the respective impingement pieces 111 will also be angularly displaced in the same direction, and the gaps 125 between adjacent impingement pieces 111 will be reduced. When the respective rotational shafts 112 are angularly displaced in the direction of the arrow E, the respective impingement pieces 111 will also be angularly displaced in the same direction, and the gaps 125 between adjacent impingement pieces will be enlarged. The size of each gap of the impingement member 58 through which the powdery material flows can be thus selected.
The powdery material having passed through the gaps 125 of the impingement member 58, constituting a classifier 63 with the above-mentioned function, has the distribution indicated by the curve 204 of Fig. 5C since the material has not been classified by the rotary blades 52. The powdery material, which enters the space 65 after the classification by the rotary blades 52 as explained in this embodiment, has the distribution indicated by the curve 203 of Fig. 5B as explained in this embodiment. These powdery materials are mixed in the space 65, etc., and produce the distribution indicated by the curve 205 of Fig. 5D.
Further, since the size of the gaps 125 of the impingement member 58 can be selected as described above, the present embodiment has a classifying capacity which allows selection of the distribution range of particle diameter with the average value of particle diameter being also selectable.
Fig. 24A is a sectional view of the vertical mill 40 of Fig. 1 near the top thereof and it is useful for explaining the operation of the classifier 63 in the embodiments hereof. In Fig. 24A, the radial distance between the axis G of rotation of the rotary blades 52 and the center of the top end of a rotary blade 52, is denoted by a. The distance between the axis G of rotation and the inner circumference or edge of the fixed annular member 54 is denoted by b. The distance between the lower face of the top plate 57 and the top face of the fixed annular member 54 is denoted by L1, and the vertical height of the rotary blade 52 is denoted by h.
It has been verified by the inventors of the present invention that the classifying effect is significant when the following formula holds for the circumferential area 2naL1 of the gap 57a and the similar area 2nbh of the rotary blades 52.
Fig. 25 is a system diagram of a controller of an embodiment of the classifier 63 of the present invention. The powdery material having been classified as explained in the above-mentioned embodiments and discharged from the outlet port 64 is then conveyed via a line 131 to a cyclone separator 130 which forms a collecting means. The cyclone 130 is connected, via a line 132 to a fan 133.
On the discharge line 134 which removes the powdery material separated from the gas stream in the cyclone 130, a conventional valve means 135 is provided having the function of preventing gas from moving from the line 134 into the cyclone 130.
On the line 134 downstream of the valve means 135, a detecting means 136 is provided which detects the distribution of the particle size of the powdery material and produces outputs which represent, for example, the tangential value N5 of Equation 6 and P4 of Fig. 5D. The powdery material which has passed through the detecting means 136 is removed as the finished product.
The output values representing N5 and P4 are fed to an adjusting means 137 which adjusts the controller of the classifier 63 so that the output . values of N5 and P4 will substantially equal the preselected values Nt and Pt. The adjusting means 137 performs the above-mentioned functions, and its outputs are electrically connected to, for example, the driving means 55 and 123 of the ninth embodiment shown in Fig. 21. Thus, when the measured values of N5 and P4 representing the distribution of the powder diameter of the powdery material, as detected by the detecting means 136, show some deviations from the preselected values of Nt and Pt, the adjusting means 137 compares the measured values with the preselected values and produces error signals at its outputs, and the error signals control the drive for adjusting the size of the gaps 125 of the classifier 63 by energizing the driving means 123, and the speed adjusting means 55 for the rotary blades 52, etc. Thus the particle size configuration of the powdery material passing through the rotary blades 52 can be automatically adjusted and held at predetermined values.
As a result, the distribution curve of the particle diameter of the powdery material being discharged from the outlet port 64 may be changed, and the gradient and the average diameter P4 of the curve 210 of Fig. 6B may be changed. The values of N5 and P4 are thus adjusted to approach the selected values of Nt and Pt.
In summary, according to the present invention, a gap is formed in an impingement member of the classifier mounted in the casing, which allows the passage of the powdery material which is not subjected to the classification by the rotary blades of the classifier. This nonclassified portion of the powdery material is then mixed with another portion of the powdery material which has been classified by the rotary blades; the range of the distribution curve of the particle diameter of the powdery material thus obtained can be selected.
Furthermore, with the control system for detecting the distribution of particle diameter of the powdery material discharged after passage through the classifier and for adjusting the size of the passage area of the gap to adjust the values characteristic of the particle size distribution to the preselected ones, the range of the distribution curve of the particle diameter can be automatically controlled.

Claims

1. A classifier for a vertical mill, the mill including an outer casing (41) having a top plate (57) and an associated exit (64) for powdery material, means (42, 44) in the lower portion of the casing for pulverising material, and means (49, 50) producing an upward flow of gas for carrying powdery material upwardly toward the top plate, said classifier comprising a rotary impeller, especially a set of impeller blades (52), in said casing adjacent said top plate and having a generally vertical axis of rotation; characterised in that said rotary impeller is spaced below said top plate to provide a gap between said rotary impeller and the top plate, and an annular impingement member (58) is mounted under the top plate and outwardly surrounding the upper portion of said rotary impeller so as to shield said gap, said annular impingement member having an opening or openings (62) associated therewith through which gas and powdery material can pass radially inwardly en route to said exit without passing through said impeller.

2. A classifier according to Claim 1, wherein said opening (62) is formed in said impingement member, and further including adjustment means (77, 95) on said impingement member for varying the flow area of said opening.

3. A classifier according to Claim 2, wherein a plurality of said openings (62) and adjustment means (77, 95) are provided.

4. A classifier according to Claim 1, wherein said impingement member is spaced from the top plate, and said opening is formed by said spacing (85) between said top plate and said impingement member.

5. A classifier according to Claim 4, and further including means (82, 83) connected to said impingement member for raising/lowering it to adjust said spacing and thereby the size of said opening.

6. A classified according to Claim 5, and further including a fixed annular shield member (87) under the top plate and disposed radially between said impingement member and the rotary impeller.

7. A classifier according to Claim 1, wherein said opening or openings are formed in said annular impingement member, and further including an obturating ring (90) surrounding and contiguous with said annular impingement member, with means (82, 83) connected to said obturating ring for raising and lowering it to vary the flow area of said opening or openings.

8. A classifier according to Claim 2 or Claim 3, wherein the adjustment means comprise an obturating slide (95) placed against the circumferential surface of the annular impingement member in which the opening or openings are formed, and means (96, 98; 100-102) for adjusting the position of the slide circumferentially to change the flow area of the opening or openings.

9. A classifier according to Claim 1, wherein said impingement member is formed by a circumferential series of plates (111), said opening or openings being formed by spaces (125) between said plates.

10. A classifier according to Claim 9, wherein said plates are each pivotally mounted for setting at varying angles in the horizontal plane, and further including means (112, 116, 118, 120-124) for adjusting the angles of said plates and thereby the flow area through said spaces between the plates.

11. A classifier according to any preceding claim, and further including detecting means (136) adapted to monitor the powdery material leaving the exit and produce an output signal or signals representative of the particle size distribution of the material, and control means (137) responsive to said output signal or signals whereby the flow area of the opening or openings associated with said impingement member is adjusted toward achieving a predetermined particle size distribution.

12. A classifier according to Claim 11, wherein said control means is also responsive to said output signal or signals to adjust the rate of rotation of said rotary impeller.

13. A vertical mill with a classifier according to Claim 11 or Claim 12, having a rotary milling table (42) and crushing rollers (44) rolling thereon in the lower portion of the casing and said classifier (63) in the upper portion of the casing, gas blast port means (49) at the lower portion of the casing, and collector means (131,130,135,134) collecting the powdery material from the exit and delivering it to the detecting means (136).

14. A mill according to Claim 13, further including a funnel-shaped cone (71) in the upper part of the casing above the milling table, and a static ring of angled classifying blades (72) disposed between the upper edge of the cone and the top plate of the casing, the rotary impeller and the annular impingement member being situated coaxially inside the region defined by the upper part of the cone and the static ring of blades, with powdery material passing through the static blades to reach the impingement member and the rotary impeller.